When one looks into architectural history, many innovative building shapes and forms can be found. These shapes represent major structural inventions of the time and are being further developed even today as functional and beautiful building solutions. One such roofing form is the dome, which can commonly be observed in old religious structures as well as in contemporary buildings. Continue reading to understand the dome meaning and explore the types of domes based on their shape, support system and materials used.
What is a Dome?
A dome is an architectural roofing structure which typically has the shape of a round or hemisphere. Domes are believed to have first been developed from arch structures during prehistoric times and can be found in ancient Mesopotamian, Chinese and Persian civilisations. However, dome architecture underwent significant advancement during ancient Roman times, when extremely long-span domes were built using stone and brick masonry. Today, these structures still remain prominent parts of buildings and are often built with modern materials like concrete and tensile fabrics.
Types of Domes
Dome structures can be classified on the basis of three major factors, as follows:
- Types of Domes Based on Support System: Two types of structures have been used to support masonry domes for many centuries, and historically allowed builders to transition from square-shaped rooms to circular roof forms efficiently. These are:
- Domes on pendentives
- Domes on squinches
- Types of Domes Based on Shape/ Form: Although typically hemispherical, dome shapes can be modified to form other related forms. Some of the commonly observed dome shapes are:
- Hemispherical dome
- Bulbous/ onion dome
- Beehive dome
- Geodesic dome
- Ellipsoidal/ oval dome
- Sail dome
- Cloistered dome
- Cross-arched dome
- Compound dome
- Types of Domes Based on Material Used: Domes can be constructed using a wide range of materials, including the following types:
- Masonry domes
- Concrete domes
- Tensile fabric domes
- Metal and glass domes
Dome Types Based on Support System
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Two types of supporting structures have commonly been used to transition from square-shaped rooms to circular dome roofs:
Image source: Link
Dome on Pendentives
Pendentives are curved triangular elements that fill the space between arches, creating a round base on which domes can rest. The structural load of the dome gets evenly distributed across each pendentive on a square base, ensuring effective stability. Aesthetically, a smooth transition is created from linear walls to the curved dome surface by using pendentives.
Dome on Squinches
In this system, a square base is transformed to an octagonal base with squinches. A corbelling system is used to slowly transition the octagon into a polygon with 16 or 32 sides, on which the dome rests. Although they are equally stable, domes on squinches are not as aesthetically pleasing as domes on pendentives since their transition is not as smooth.
However, these two types have been used historically for supporting masonry dome structures. Today, many new and more advanced techniques for supporting dome structures—including self-supporting domes, inflatable domes and metal framed domes—are used.
Types of Domes Based on Shape/ Form
Hemispherical Dome
A hemispherical dome is one of the simplest dome types and consists of one half of a sphere. This dome is visually pleasing, extremely symmetrical and stable, thus requiring lower supporting elements than other complex dome forms. Such a dome is typically supported by a ring-shaped beam at its base, which rests on load-bearing walls, squinches, pendentives or columns.
Bulbous Dome/ Onion Dome
Bulbous domes have a middle surface that bulges out from their base diameter along with a pointed top, resembling the shape of an onion. This type of dome has an S-shaped or ogee profile, creating a form that is much higher than a hemispherical dome. Onion domes can commonly be observed in mosques and other religious buildings, where they often have colourfully painted surfaces.
Beehive Dome
Beehive domes have pointed tops and are made by corbelling (each horizontal layer of masonry blocks is cantilevered until the layers meet at a central point at the top to create a pyramidical structure). These domes are not considered true domes as they do not exactly have curved surfaces. They are commonly referred to as false domes or corbelled domes.
Geodesic Dome
A geodesic dome is formed by arranging multiple layers of triangles in a circular layout such that they finally meet at a central point on top. These dome-shaped structures were developed in the 20th century by Buckminster Fuller. They have extreme structural stability and can be constructed easily with frameworks made of metals like mild steel and aluminium.
Ellipsoidal/ Oval Dome
An elliptical/ ellipsoidal/ oval dome has a shape resembling an egg and represents a cut segment of a sphere. Such dome-shaped structures are used to create long-span roofs without increasing the height too much and without the necessity of intermediate columns. They are commonly used to form the roofs of sports arenas or stadiums.
Sail Dome
Sail domes or sail vaults are formed by pendentives that directly rise up to form a curved roofing surface. Such dome roofs can be built with low heights and lesser expenditure on support structures, as the dome itself is self-supported. They are commonly referred to as domical vaults or pendentive domes and create smooth and aesthetically pleasing interior spaces.
Cloistered Dome
Cloistered domes are formed by a series of pointed, triangular or rounded arches which intersect at a center point. These arches create segmented portions or ‘cloisters’ in the interior surface of the roofs, producing intricate patterns. Although they are not perfectly round structures, this type of dome has commonly been used to form the roofs of many prominent historical buildings.
Cross-Arched Dome
A cross-arched dome is formed by multiple arches or vaults that intersect each other off-centre. Numerous polygonal segments or portions are formed on the interior surface of this arch and dome structure, creating intricate ceiling designs. Commonly called ribbed domes, these structures have typically been used in religious and institutional buildings in the past.
Compound Dome
Compound domes have a small dome that rests on pendentives or drums with larger diameters, often forming a structure that looks like two domes placed one above the other. Although they look extremely intricate and beautiful, these dome types have a much larger height than the other types and can be more complicated to build.
Types of Domes Based on Material
Masonry Domes
Brick and stone masonry have been used to build domes for thousands of years. In such domes, each layer of bricks or stones is laid in concentric layers that meet in the centre on top (corbelling system). Although mortar joints are generally used to bond the masonry units, they have been joined together by interlocking systems in many historical buildings.
Concrete Domes
RCC (Reinforced Cement Concrete) can be used to build monolithic domes. Such domes often have foam insulation and are extremely durable. However, the formwork and reinforcement for concrete domes can be difficult to achieve and are expensive. Short-span and extremely thin domes can be created by using ferrocement, which can also be more cost-effective and produce smoother surfaces.
Tensile Fabric Domes
Different types of plastic materials, such as PVC-coated polyester and PVDF (Polyvinylidene Fluoride), can be used to make tensile fabric domes that are either self-supporting or supported by cables and anchors. These plastic domes are extremely lightweight, cost-effective and easy to erect. They can also be designed to be flexible and/ or inflatable.
Metal and Glass Domes
Modern dome structures, such as geodesic domes, are often made with a metal (generally steel or aluminium) framework and glass (or similar materials) infill panels. Such domes are quick and easy to construct and also maximise natural light in interior spaces. Polycarbonate (a type of plastic) is often used as a substitute for glass, as polycarbonate domes are much more lightweight and impact-resistant.
Getting a Dome Structure Built
Even with the advanced construction technologies available today, dome houses and structures require skilled labour and the use of quality materials to ensure structural stability. Brick & Bolt is a leading construction company in India that collaborates with experienced designers and contractors to guarantee the success of dome structures. The company also offers a streamlined building materials supply in its projects, which is complemented by a patented quality checking system (QASCON) to assure premium quality in construction. To get different types of domes designed and built for your residential or commercial project, reach out to Brick & Bolt today!
Apoorva H P Achar